Source

cffi / cffi / api.py

import types

class FFIError(Exception):
    pass

class CDefError(Exception):
    def __str__(self):
        try:
            line = 'line %d: ' % (self.args[1].coord.line,)
        except (AttributeError, TypeError, IndexError):
            line = ''
        return '%s%s' % (line, self.args[0])


class FFI(object):
    r'''
    The main top-level class that you instantiate once, or once per module.

    Example usage:

        ffi = FFI()
        ffi.cdef("""
            int printf(const char *, ...);
        """)

        C = ffi.dlopen(None)   # standard library
        -or-
        C = ffi.verify()  # use a C compiler: verify the decl above is right

        C.printf("hello, %s!\n", ffi.new("char[]", "world"))
    '''

    def __init__(self, backend=None):
        """Create an FFI instance.  The 'backend' argument is used to
        select a non-default backend, mostly for tests.
        """
        from . import cparser
        if backend is None:
            try:
                import _cffi_backend as backend
            except ImportError as e:
                import warnings
                warnings.warn("import _cffi_backend: %s\n"
                              "Falling back to the ctypes backend." % (e,))
                from . import backend_ctypes
                backend = backend_ctypes.CTypesBackend()
        self._backend = backend
        self._parser = cparser.Parser()
        self._cached_btypes = {}
        self._parsed_types = types.ModuleType('parsed_types').__dict__
        self._new_types = types.ModuleType('new_types').__dict__
        self._function_caches = []
        self._cdefsources = []
        self._pointer_type_cache = {}
        if hasattr(backend, 'set_ffi'):
            backend.set_ffi(self)
        #
        lines = []
        by_size = {}
        for cname in ['long long', 'long', 'int', 'short', 'char']:
            by_size[self.sizeof(cname)] = cname
        for name, size in self._backend.nonstandard_integer_types().items():
            if size & 0x1000:   # unsigned
                equiv = 'unsigned %s'
                size &= ~0x1000
            else:
                equiv = 'signed %s'
            lines.append('typedef %s %s;' % (equiv % by_size[size], name))
        self.cdef('\n'.join(lines))
        del self._cdefsources[:]
        #
        self.NULL = self.cast("void *", 0)
        self.CData, self.CType = backend._get_types()

    def cdef(self, csource, override=False):
        """Parse the given C source.  This registers all declared functions,
        types, and global variables.  The functions and global variables can
        then be accessed via either 'ffi.dlopen()' or 'ffi.verify()'.
        The types can be used in 'ffi.new()' and other functions.
        """
        self._parser.parse(csource, override=override)
        self._cdefsources.append(csource)
        if override:
            for cache in self._function_caches:
                cache.clear()

    def dlopen(self, name):
        """Load and return a dynamic library identified by 'name'.
        The standard C library can be loaded by passing None.
        Note that functions and types declared by 'ffi.cdef()' are not
        linked to a particular library, just like C headers; in the
        library we only look for the actual (untyped) symbols.
        """
        assert isinstance(name, str) or name is None
        lib, function_cache = _make_ffi_library(self, name)
        self._function_caches.append(function_cache)
        return lib

    def _typeof(self, cdecl, consider_function_as_funcptr=False):
        # string -> ctype object
        try:
            btype, cfaf = self._parsed_types[cdecl]
            if consider_function_as_funcptr and not cfaf:
                raise KeyError
        except KeyError:
            cfaf = consider_function_as_funcptr
            type = self._parser.parse_type(cdecl,
                       consider_function_as_funcptr=cfaf)
            btype = self._get_cached_btype(type)
            self._parsed_types[cdecl] = btype, cfaf
        return btype

    def typeof(self, cdecl):
        """Parse the C type given as a string and return the
        corresponding Python type: <class 'ffi.CData<...>'>.
        It can also be used on 'cdata' instance to get its C type.
        """
        if isinstance(cdecl, str):
            return self._typeof(cdecl)
        else:
            return self._backend.typeof(cdecl)

    def sizeof(self, cdecl):
        """Return the size in bytes of the argument.  It can be a
        string naming a C type, or a 'cdata' instance.
        """
        if isinstance(cdecl, str):
            BType = self._typeof(cdecl)
            return self._backend.sizeof(BType)
        else:
            return self._backend.sizeof(cdecl)

    def alignof(self, cdecl):
        """Return the natural alignment size in bytes of the C type
        given as a string.
        """
        if isinstance(cdecl, str):
            cdecl = self._typeof(cdecl)
        return self._backend.alignof(cdecl)

    def offsetof(self, cdecl, fieldname):
        """Return the offset of the named field inside the given
        structure, which must be given as a C type name.
        """
        if isinstance(cdecl, str):
            cdecl = self._typeof(cdecl)
        return self._backend.typeoffsetof(cdecl, fieldname)[1]

    def new(self, cdecl, init=None):
        """Allocate an instance according to the specified C type and
        return a pointer to it.  The specified C type must be either a
        pointer or an array: ``new('X *')`` allocates an X and returns
        a pointer to it, whereas ``new('X[n]')`` allocates an array of
        n X'es and returns an array referencing it (which works
        mostly like a pointer, like in C).  You can also use
        ``new('X[]', n)`` to allocate an array of a non-constant
        length n.

        The memory is initialized following the rules of declaring a
        global variable in C: by default it is zero-initialized, but
        an explicit initializer can be given which can be used to
        fill all or part of the memory.

        When the returned <cdata> object goes out of scope, the memory
        is freed.  In other words the returned <cdata> object has
        ownership of the value of type 'cdecl' that it points to.  This
        means that the raw data can be used as long as this object is
        kept alive, but must not be used for a longer time.  Be careful
        about that when copying the pointer to the memory somewhere
        else, e.g. into another structure.
        """
        if isinstance(cdecl, str):
            cdecl = self._typeof(cdecl)
        return self._backend.newp(cdecl, init)

    def cast(self, cdecl, source):
        """Similar to a C cast: returns an instance of the named C
        type initialized with the given 'source'.  The source is
        casted between integers or pointers of any type.
        """
        if isinstance(cdecl, str):
            cdecl = self._typeof(cdecl)
        return self._backend.cast(cdecl, source)

    def string(self, cdata, maxlen=-1):
        """Return a Python string (or unicode string) from the 'cdata'.
        If 'cdata' is a pointer or array of characters or bytes, returns
        the null-terminated string.  The returned string extends until
        the first null character, or at most 'maxlen' characters.  If
        'cdata' is an array then 'maxlen' defaults to its length.

        If 'cdata' is a pointer or array of wchar_t, returns a unicode
        string following the same rules.

        If 'cdata' is a single character or byte or a wchar_t, returns
        it as a string or unicode string.

        If 'cdata' is an enum, returns the value of the enumerator as a
        string, or "#NUMBER" if the value is out of range.
        """
        return self._backend.string(cdata, maxlen)

    def buffer(self, cdata, size=-1):
        """Return a read-write buffer object that references the raw C data
        pointed to by the given 'cdata'.  The 'cdata' must be a pointer or
        an array.  To get a copy of it in a regular string, call str() on
        the result.
        """
        return self._backend.buffer(cdata, size)

    def callback(self, cdecl, python_callable=None, error=None):
        """Return a callback object or a decorator making such a
        callback object.  'cdecl' must name a C function pointer type.
        The callback invokes the specified 'python_callable' (which may
        be provided either directly or via a decorator).  Important: the
        callback object must be manually kept alive for as long as the
        callback may be invoked from the C level.
        """
        def callback_decorator_wrap(python_callable):
            if not callable(python_callable):
                raise TypeError("the 'python_callable' argument "
                                "is not callable")
            return self._backend.callback(cdecl, python_callable, error)
        if isinstance(cdecl, str):
            cdecl = self._typeof(cdecl, consider_function_as_funcptr=True)
        if python_callable is None:
            return callback_decorator_wrap                # decorator mode
        else:
            return callback_decorator_wrap(python_callable)  # direct mode

    def getctype(self, cdecl, replace_with=''):
        """Return a string giving the C type 'cdecl', which may be itself
        a string or a <ctype> object.  If 'replace_with' is given, it gives
        extra text to append (or insert for more complicated C types), like
        a variable name, or '*' to get actually the C type 'pointer-to-cdecl'.
        """
        if isinstance(cdecl, str):
            cdecl = self._typeof(cdecl)
        replace_with = replace_with.strip()
        if (replace_with.startswith('*')
                and '&[' in self._backend.getcname(cdecl, '&')):
            replace_with = '(%s)' % replace_with
        elif replace_with and not replace_with[0] in '[(':
            replace_with = ' ' + replace_with
        return self._backend.getcname(cdecl, replace_with)

    def gc(self, cdata, destructor):
        """Return a new cdata object that points to the same
        data.  Later, when this new cdata object is garbage-collected,
        'destructor(old_cdata_object)' will be called.
        """
        try:
            gc_weakrefs = self.gc_weakrefs
        except AttributeError:
            from .gc_weakref import GcWeakrefs
            gc_weakrefs = self.gc_weakrefs = GcWeakrefs(self)
        return gc_weakrefs.build(cdata, destructor)

    def _get_cached_btype(self, type):
        try:
            BType = self._cached_btypes[type]
        except KeyError:
            finishlist = []
            BType = type.get_cached_btype(self, finishlist)
            for type in finishlist:
                type.finish_backend_type(self, finishlist)
        return BType

    def verify(self, source='', tmpdir=None, **kwargs):
        """Verify that the current ffi signatures compile on this
        machine, and return a dynamic library object.  The dynamic
        library can be used to call functions and access global
        variables declared in this 'ffi'.  The library is compiled
        by the C compiler: it gives you C-level API compatibility
        (including calling macros).  This is unlike 'ffi.dlopen()',
        which requires binary compatibility in the signatures.
        """
        from .verifier import Verifier, _caller_dir_pycache
        tmpdir = tmpdir or _caller_dir_pycache()
        self.verifier = Verifier(self, source, tmpdir, **kwargs)
        return self.verifier.load_library()

    def _get_errno(self):
        return self._backend.get_errno()
    def _set_errno(self, errno):
        self._backend.set_errno(errno)
    errno = property(_get_errno, _set_errno, None,
                     "the value of 'errno' from/to the C calls")

    def addressof(self, cdata, field=None):
        """Return the address of a <cdata 'struct-or-union'>.
        If 'field' is specified, return the address of this field.
        """
        ctype = self._backend.typeof(cdata)
        ctype, offset = self._backend.typeoffsetof(ctype, field)
        try:
            ctypeptr = self._pointer_type_cache[ctype]
        except KeyError:
            ctypeptr = self._pointer_type_cache[ctype] = (
                self._typeof(self.getctype(ctype, '*')))
        return self._backend.rawaddressof(ctypeptr, cdata, offset)


def _make_ffi_library(ffi, libname):
    name = libname
    if name is None:
        name = 'c'    # on Posix only
    if '/' in name:
        path = name
    else:
        import ctypes.util
        path = ctypes.util.find_library(name)
        if path is None:
            raise OSError("library not found: %r" % (name,))
    #
    backend = ffi._backend
    backendlib = backend.load_library(path)
    #
    def make_accessor(name):
        key = 'function ' + name
        if key in ffi._parser._declarations:
            tp = ffi._parser._declarations[key]
            BType = ffi._get_cached_btype(tp)
            value = backendlib.load_function(BType, name)
            library.__dict__[name] = value
            return
        #
        key = 'variable ' + name
        if key in ffi._parser._declarations:
            tp = ffi._parser._declarations[key]
            BType = ffi._get_cached_btype(tp)
            read_variable = backendlib.read_variable
            write_variable = backendlib.write_variable
            setattr(FFILibrary, name, property(
                lambda self: read_variable(BType, name),
                lambda self, value: write_variable(BType, name, value)))
            return
        #
        raise AttributeError(name)
    #
    class FFILibrary(object):
        def __getattr__(self, name):
            make_accessor(name)
            return getattr(self, name)
        def __setattr__(self, name, value):
            try:
                property = getattr(self.__class__, name)
            except AttributeError:
                make_accessor(name)
                setattr(self, name, value)
            else:
                property.__set__(self, value)
    #
    if libname is not None:
        FFILibrary.__name__ = 'FFILibrary_%s' % libname
    library = FFILibrary()
    return library, library.__dict__
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